Modified my version of AC_ISC_POSIX to not set the CC variable, in case the user or configure script has already set it.
Modified my version of AC_ISC_POSIX to not set the CC variable, in case
the user or configure script has already set it.

svn path=/trunk/; revision=1228

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot